Nanomolar Levels of Dimethylsulfoniopropionate, Dimethylsulfonioacetate, and Glycine Betaine Are Sufficient To Confer Osmoprotection to Escherichia coli

Abstract

We combined the use of low inoculation titers (300 ± 100 CFU/ml) and enumeration of culturable cells to measure the osmoprotective potentialities of dimethylsulfoniopropionate (DMSP), dimethylsulfonioacetate (DMSA), and glycine betaine (GB) for salt-stressed cultures of Escherichia coli. Dilute bacterial cultures were grown with osmoprotectant concentrations that encompassed the nanomolar levels of GB and DMSP found in nature and the millimolar levels of osmoprotectants used in standard laboratory osmoprotection bioassays. Nanomolar concentrations of DMSA, DMSP, and GB were sufficient to enhance the salinity tolerance of E. coli cells expressing only the ProU high-affinity general osmoporter. In contrast, nanomolar levels of osmoprotectants were ineffective with a mutant strain (GM50) that expressed only the low-affinity ProP osmoporter. Transport studies showed that DMSA and DMSP, like GB, were taken up via both ProU and ProP. Moreover, ProU displayed higher affinities for the three osmoprotectants than ProP displayed, and ProP, like ProU, displayed much higher affinities for GB and DMSA than for DMSP. Interestingly, ProP did not operate at substrate concentrations of 200 nM or less, whereas ProU operated at concentrations ranging from 1 nM to millimolar levels. Consequently,proU + strains of E. coli, but not the proP + strain GM50, could also scavenge nanomolar levels of GB, DMSA, and DMSP from oligotrophic seawater. The physiological and ecological implications of these observations are discussed.

Molecular dissection of bacterial acrylate catabolism – unexpected links with dimethylsulfoniopropionate catabolism and dimethyl sulfide production

“…As expected (Cosquer et al, 1999), DMSP conferred tolerance to NaCl in wild-type E. coli MC4100 but not to the MKH13 mutant. This defect was fully corrected by the cloned dddT gene in pBIO1693 confirming that DddT can import DMSP.…”

“…So, different strains likely acquired their particular version of the BCCT family by HGT from different sources. The conventional BCCT-type transporter of E. coli imports DMSP as well as its more conventional substrates (Cosquer et al, 1999), so no major changes were needed for these regular BCCT-type transporters to evolve when the corresponding genes were amalgamated into the dddD clusters of different DMSP-catabolising bacteria. This 'pick'n mix' arrangement of transporter genes near dddD in different bacteria is more vividly exemplified by the fact that near dddD in Rhizobium NGR234 and Burkholderia ambifaria there are genes that encode DMSP transporters, but these are in the ABC family, completely different from the BCCT type .…”

“…This plasmid was transformed into E. coli MKH13, which is multiply defective in betaine uptake due to mutations in proU and proP (Haardt et al, 1995). As shown in Table 3, the MKH13 mutant was markedly reduced in [1-14 C]DMSP uptake compared with its wild-type parent, E. coli MC4100, confirming that E. coli itself can import DMSP via its conventional betaine transport systems (Cosquer et al, 1999). However, the cloned Halomonas dddT gene in pBIO1693 restored DMSP uptake to MKH13; indeed, DMSP import rates were greater in MKH13/pBIO1693 than in the wildtype MC4100.…”

The ATP-binding cassette transporter Cbc (choline/betaine/carnitine) recruits multiple substrate-binding proteins with strong specificity for distinct quaternary ammonium compounds

“…A similar lack of inhibition was reported for the transporter ChoXWV (Dupont et al, 2004) and its orthologue GbcXWV (Fox et al, 2008). This lack of competition by one substrate against another substrate has not been observed in osmoregulatory QAC transporters, such as E. coli ProU (Cosquer et al, 1999a) and P. syringae OpuC (Chen and Beattie, 2007), and probably contributed to the initial conclusion that betaine was not a substrate for the Cho transporter. Such a lack of competition in uptake can be explained by better adaptation of ChoX, and potentially CbcX, to bind choline than betaine (Dupont et al, 2004); for example, perhaps choline binding induces a conformational change that excludes betaine binding.…”

Abiotic stress protection by ecologically abundant dimethylsulfoniopropionate and its natural and synthetic derivatives: insights fromBacillus subtilis

“…It is, however, best known for its role as an osmolyte for the producer organisms (Stefels, 2000), most of which live in high-saline environments (Yoch, 2002;Curson et al, 2011a;Reisch et al, 2011;Moran et al, 2012). Notably, osmostress protection by DMSP can also be conferred through its uptake by microorganisms that do not produce it (Gouesbet et al, 1994;Pichereau et al, 1998;Cosquer et al, 1999;Bayles and Wilkinson, 2000;Murdock et al, 2014).…”